Inelastic neutron scattering and measurement of the ortho-para separation coefficient have been used to study the low lying rotational states of molecular hydrogen adsorbed on activated alumina. The observations are consistent with a picture in which the orientational motion of the molecules is severely hindered. Results are analyzed in terms of two models: a two-dimensional rotor and an axially constrained rotor. The latter which is more consistent with the data serves to explain preferential adsorption of orthohydrogen.
Physical Review Letters, 1976, Vol 37, Issue 19, p. 1275-1278